One reason why polling companies can't get usable info is that end users tend to be constantly barraged by robocalls,
I suspect that another reason, particularly when you're talking mobile, is that people who answer phones are far less likely to be sitting in a nice, comfortable chair in their living room ready to play 20 questions with whoever calls. If my parents call while I'm out walking the dog or something, I'll chat for a few minutes. If a pollster calls, they're out-of-luck.
The business model of polling is dependent on the willingness of strangers to let pollsters suck away a few minutes of their time for free, and people... just have too much other stuff happening.
Plus, if I'm talking with some Luddite on the phone, how can I check Facebook?